Improved micro-flame detection method for gas chromatography

A previously developed micro-counter-current flame method is modified to provide both sensitive photometric and ionization detection for gas chromatography (GC). A stainless steel capillary (0.254 mm i.d.) supplying oxygen functions as a burner, which supports a compact flame that burns in a counter-flowing excess of hydrogen. In the "micro-flame photometric detector" ((mu)FPD) response mode, the background emission level is reduced by over an order of magnitude compared to previous experiments using a fused silica capillary burner, resulting in greatly improved detection limits. Chemiluminescent sulfur response in the (mu)FPD is quadratic over 3.5 orders of magnitude, yielding a detection limit of 3 × 10^-11 gS/s, while that of phosphorus is linear over 5 orders of magnitude down to a minimum detectable limit of 3 × 10^-12 gP/s. Tin response is examined for the first time in the (mu)FPD and yields a blue luminescence (ascribed to SnO*) on the surface of the quartz flame enclosure. Although this emission provides a sensitive detection limit near 6 × 10^-15 gSn/s, due to the limited surface area within the detector cell it only produces a linear response range of one order of magnitude. Ionization response toward hydrocarbons is also obtained from the hydrogen-rich micro-counter-current flame. A linear response is produced over five orders of magnitude, yielding a detection limit toward carbon of 2 × 10^-10 gC/s. Analysis of a simple gasoline sample is used to demonstrate that the device can successfully operate as both a selective and universal GC detector. Results indicate that this micro-counter-current flame method yields comparable performance to conventional flame photometric and flame ionization detectors, making it potentially useful for adaptation to micro-analytical devices and portable GC units.